ON THE ANATOMY AND DEVELOPMENT OF PYROSOMA = 373 
The stolons are zigth of an inch long; they pass almost hori- 
zontally inwards, towards the rudimentary lip of the cloaca, and are 
curved towards its cavity, at their blind extremities. The corpuscles 
of which their walls are composed are more elongated than before 
and, sending processes into the adjacent substance of the test, cause 
the czcal ends of the stolons to have a very peculiar, brushlike 
appearance. 
3. Lhe Test—As I propose to reserve the description of the histo- 
logical changes undergone by the embryo of Pyrosoma for another 
occasion, I will merely state, in this place, that the test appears, at 
first, to be a structureless excretion. Subsequently, cellular bodies, 
like connective-tissue corpuscles, are discernible in its most superficial 
layer, and are disposed in such a manner as to form a very regular, 
hexagonal network, with large meshes. The most advanced fcetus 
has presented neither of the fibrous layers visible in the adult test. 
Ninth Stage. The conversion of the tetrazooidal fetus tnto the 
adult ascidiarium. 
The most advanced foetus which has been described differs from 
the adult ascidiarium not merely in size, in the paucity of its ascidio- 
zooids, in the form and proportions of the latter, in the absence of 
buds, or ever so slightly differentiated reproductive organs, in them, 
and in their large atrial apertures (all of which are peculiarities which 
we may easily conceive to be altered by age and growth), but in still 
more important characters, seeing that in the adult ascidiarium I have 
met with no trace of the cyathozooid or the isthmuses, nor have I 
been able to discover any ascidiozooid with two stolons. 
The first theory of the mode of formation of the adult ascidiarium 
which suggests itself is obviously that which supposes that the four 
ascidiozooids of the fcetus give rise, by budding, to all those of 
the adult Pyrosoma, at the same time losing the two stolons, and 
acquiring reproductive organs, so as to be undistinguishable from 
their agamogenetic progeny. 
But difficulties arise when we compare this theoretical conception 
with the structural characters, and the ascertained laws of gemmation 
of Pyrosoma. 
In every ascidiozooid of the adult ascidiarium (and there is no 
reason to suppose that those of the tetrazooidal foetus constitute 
exceptions to the rule) budding takes place, as we have seen, from 
a single definite region of the body, situated in the posterior moiety 
